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US federal law enforcement agencies have obtained access to clear text copies of encrypted emails sent through Hushmail as part a of recent drug trafficking investigation.

The access was only granted after a court order was served on Hush Communications, the Canadian firm that offers the service.

Hush Communications said it would only accede to requests made in respect to targeted accounts and via court orders filed through Canadian court.

Nonetheless, the incident illustrates that Hushmail's marketing claims that not even its own staff can access encrypted email is well wide of the mark.

September court documents (pdf) from a US federal prosecution of alleged steroid dealers reveals that Hush turned over 12 CDs involving emails on three targeted Hushmail accounts, in compliance of court orders made through the mutual assistance treaty between the US and Canada.

Hushmail is widely used by privacy advocates and the security-conscious to send confidential emails. The service uses robust cryptographic and encryption protocols (OpenPGP and AES 256) to scramble the contents of messages stored on its servers, and to exchange encrypted messages with other encrypted email users.

Breaking messages encrypted by the service by brute force would be nigh-on impossible. So how was access to clear-text messages obtained? An investigation by Wired reveals that a server-side encryption option introduced by Hushmail in 2006 means that a copy of a user's passphrase, which gives access to encrypted messages, might be obtained.

"In the case of the alleged steroid dealer, the feds seemed to compel Hushmail to exploit this hole, store the suspects' secret passphrase or decryption key, decrypt their messages, and hand them over," Wiredreports.

Brewing up a storm

Hushmail introduced the server-side encryption option because some users found installing and running a Java applet to be slow and annoying. In its original form this Java applet was used to perform the encryption and decryption of messages on a user's computer.

In this scenario, a clear text copy of a message would never hit Hushmail's servers so Hush would only be able to respond to law enforcement requests with scrambled messages, at least in theory. In practice, Hushmail's Java architecture still permits a mechanism for the recovery of scrambled emails in clear-text form.

Brian Smith, chief technology officer of Hushmail, declined to speak about specific law enforcement requests. However he was more forthcoming in explaining the technology implications of Hushmail's server-side encryption options.

"The key point, though, is that in the non-Java configuration, private key and passphrase operations are performed on the server-side. This requires that users place a higher level of trust in our servers as a trade off for the better usability they get from not having to install Java and load an applet," he said.

"This might clarify things a bit when you are considering what actions we might be required to take under a court order. Again, I stress that our requirement in complying with a court order is that we not take actions that would affect users other than those specifically named in the order."

As Wired notes, Hushmail's marketing collateral fails to stress the implications of using the non-Java option. Even the Java option might not be entirely secure. Hush may be obliged to rig the Java applet sent to targeted users with a backdoor designed to capture their passwords, Wired implies.

It explains that "Hushmail's own threat matrix includes this possibility, saying that if an attacker got into Hushmail's servers, they could compromise an account - but that 'evidence of the attack' (presumably the rogue Java applet) could be found on the user's computer."